Study of radiation field in mesoscopic structure by using photoreactive probes

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We have investigated the state of multiple-scattered light in random media by using optical memory effect due to interference of multiple-scattered light. We have shown that the hole shape observed in this effect is equivalent to the intensity correlation function. <I(ω)I(ω+Δω)>, which is expressed by using the distribution function of the arrival time of light F(t) as |∫^^∞__0F(t)exp(iΔωt)dt|^2 + <I>^2. Therefore the frequency resolution is inversely proportional to the stay time of light in the medium. Since the stay time is approximately given by L^2/D, where L is the sample thickness, and D is the diffusion constant of light, the frequency resolution is expected to be higher for stronger scatterers. We have confirmed this prediction by using titanium oxide particles as scatterers and controlling the mean free path of light by changing its concentration. However, a deviation from the relation was observed for very strong scatterers, where the behavior of light cannot be described probably due to the weak localization of light. Thus we have established that optical memory effect due to interference of multiple-scattered light is very useful for the investigation of light in random media.